What is the difference between named credential, external credential & Auth. provider?

Hello@Sthita Pragyan Nayak,

• An external credential represents the details of how Salesforce authenticates to an external system via an authentication protocol. It also links to a user’s permission set.
• A named credential specifies the URL of a callout endpoint and its required authentication parameters in one definition. A named credential can be specified as an endpoint to simplify the setup of authenticated callouts. Named credentials connect to external credentials.
•   Please check, 

• https://help.salesforce.com/s/articleView?id=sf.external_services_define_named_credential.htm&type=5